变频调速中变频器的作用是将交流供电电源变成（）的电源。
A、变压变频
B、变压不变频
C、变频不变压
D、不变压不变频
参考答案：A
词类转换 根据所给词汇，填入一个正确的形式。
1. Edison kept _______ out his new idea.(try)
2. Do you think the computer today is _______ inventions?(useful)
3. I saw a boy ________ on the railway tracks near the station.(play)
4. I want to learn how to run quickly and to eat _______.(health)
5. She speaks too quietly.Tell her ______ a little louder.(speak)
股份有限公司的股份采取（）的形式。
A.股票
B.基金
C.债券
D.票据
